1. Field of the Invention
The present invention relates to a pattern evaluation method, a computer-readable medium, and a semiconductor device manufacturing method.
2. Related Background Art
A method of detecting an edge of an evaluation target pattern to evaluate a shape of the pattern has been extensively adopted in various industrial fields. For example, a method of using an SEM (Scanning Electron Microscope) image as a pattern examination image to evaluate a shape of a processed device pattern and thereby judge whether the pattern is good or bad is utilized in evaluation of a pattern of a semiconductor device. A procedure of measuring a CD (Critical Dimension) based on this method will be explained hereinafter as a conventional technology.
At first, an SEM image at a predetermined position on a wafer is acquired as an examination image by a CD SEM. This image includes a specific pattern as an evaluation target.
At second, one or more ROIs (Regions of Interest) are set so as to include a pattern of interest in the SEM image, edges of the patterns in the ROIs are detected based on, e.g., a threshold method, a dimension between the edges is calculated, and an obtained result is output as a CD value. The thus obtained one or more dimension values are collated with a separately determined standard to judge pass-fail of the evaluation target pattern.
According to the conventional technology, since an accuracy of a measurement value is dependent on a magnification of an image, there is a problem that a desired measurement accuracy cannot be obtained when the magnification must be reduced for various reasons. When intentionally reducing a magnification of an image in pattern measurement, the following cases can be quoted, for example.    1. When a shrinking effect should be reduced by suppressing electron beam irradiation damages given to a resist pattern as much as possible.    2. When an image having a higher image quality should be obtained by reducing charging.    3. When as many measurement points as possible should be put in one image in order to reduce the number of acquired images.    4. When patterns which are apart from each other and would protrude from an image acquiring region with a high magnification should be measured.    5. When a central part alone of an image excluding a peripheral region should be measured since the peripheral region of an image acquiring region has a large image distortion.
A size, i.e., a magnification of the image acquiring region can be determined in accordance with each of the purposes. On the other hand, measuring an image acquired with a high magnification is of course preferable in order to improve measurement accuracy. However, considering the fact that an electron beam diameter is approximately 3 nm, a higher magnification beyond this value is meaningless as an image resolution, and there is a problem that an influence of degradation in an image due to, e.g., charging of an electron beam is exercised.